1. Field of the Invention
The present invention relates to a scalable codec system, and more particularly, to an encoder and decoder to encode a signal into a scalable codec and decode the scalable codec, and encoding and decoding methods of encoding a signal into a scalable codec and decoding the scalable codes using a bitstream with a layered structure of the scalable codec.
2. Description of the Related Art
A layered structure represents that a data section of a bitstream is formed of a plurality of layers according to the G.729EV standard or a bit sliced arithmetic coding (BSAC) scheme. In the G.729EV standard, a core layer contains a minimal set of necessary data, and an enhancement layer contains data for enhancing sound quality of the core layer and is divided into eleven layers, as illustrated in FIGS. 1A and 1B. When the bitstream with a layered structure is transmitted, lower layers may be truncated from the bitstream by a bitstream truncation module in terminals or networks and only remaining higher layers may be transmitted, as occasion demands.
When a communication is performed using the bitstream having the layered structure and a traffic on a network increases in various bottleneck situations as illustrated in FIGS. 1C to 1E, the communication does not operate smoothly. If a bottleneck occurs on the network, the bitstream truncation module truncates the lower layers from the received bitstream and transmits only the remaining higher layers.
Therefore, there is a problem in that encoders encoding input signals into the layered structure should redundantly encode the lower layers that might be truncated depending on the network status. In addition, since a top coding bit rate for encoding the input signals is fixed, there is a problem in that the encoding is not optimized independent of the network status and the sound quality is deteriorated accordingly.